DIAGN MICROBIOLINFECTDIS 1991;14:53-61
53
Comparative Antimicrobial Activity of Ceftibuten Against Multiply-Resistant Microorganisms from Belgium Ludo Verbist, Jan Jacobs, and Koen Hens
To study the activity of ceftibuten, we obtained multiply-resistant isolates from -20 hospitals in Belgium. Against Enterobacteriaceae, all of the tested comparative compounds were more active than cefaclor, and ceftibuten and tigemonam were the most active of the agents tested. Ceftibuten MICsos were 41 i~g/ml for most enteric bacilli species and 85% of strains were susceptible (48 i~g/ml). This level of activity compared favorably to that recorded for cefaclor (48 I~g/ml), cefetamet (44 I~g/ml), and cefteram (41 i~g/ml), that is, 37%, 69%, and 59%, respectively. Ceftibuten, cefetamet, cefteram, and tigemonam were highly active against isolates 0f Haemophilus influenzae and Neisseria gonorrhoeae. None of the comparative agents were as ac-
tive as cefaclor against staphylococcal isolates. Against streptococci, cefleram was the most active, and tigemonam the least active of the agents. The MICgos of ceftibuten for strains of Streptococcus pneumoniae and Streptococcus pyogenes were 2 i~g/ml and 0.5 i~g/ml, respectively. Strains of Streptococcus agalactiae were resistant to both ceflibuten and tigemonam; cefaclor and cefleram inhibited 100% of isolates of this species. Strains 0f Enterococcus faecalis and Pseudomonas aeruginosa were consistently resistant to all of the compounds. Overall, ceftibuten exhibited potent activity against many multiply-resistant clinical isolates.
INTRODUCTION
Escherichia coli, Haemophilus influenzae, Klebsiella spp., Morganella morganii, Proteus spp., Providencia spp., and Serratia spp. (Hamashima et al., 1987; Jones and Barry, 1988a, c, and d). Some investigational, orally absorbed, third-generation cephems, such as cefixime and cefteram, exhibit antimicrobial activity similar to that of ceftibuten (Chau et al., 1987; Fass and Helsel, 1986; Jones and Barry, 1988a and d; N e u et al., 1986; Wise et al., 1986). However, ceftibuten is absorbed especially well, resulting in better drug bioavailability than that attained with comparative compounds (Fuchs et al., 1986; Guay et al., 1986; Nakashima et al., 1988; Shimada et al., 1986). A single 200-mg dose given to volunteers provides mean maximum plasma concentrations of 11.6 ~g/ml and has a half-life of - 1 . 9 hr (Nakashima et al., 1988); -65% of therapeutic concentrations of ceftibuten are bound to serum proteins (Nakashima et al., 1988). Ceftibuten is stable to degradation by certain [~-lactamases, including those that can hydrolyze such early-generation cephalosporins as cefaclor and cephaloridine (Jones and Barry, 1988d). A study was undertaken to compare the in vitro activity of ceftibuten with that of other orally absorbed ~-lactam antibiotics, namely, cefaclor, cefetamet, cefteram, and tigemonam. In particular, ce-
Ceftibuten is a novel, orally administered cephalosporin. Unlike such investigational oral cephems as cefetamet and cefteram, gastrointestinal absorption of ceftibuten is achieved without inclusion of an ester in this agent's chemical structure (Hamashima et al., 1987; Shimada et al., 1986; Wise et al., 1986). This structural difference has proven to be advantageous over other nonesterified, orally absorbed cephalosporins, such as cephadroxil, cefaclor, cefixime, and BMY-28100, by demonstrating either enhanced pharmacokinetics or potency against certain Gram-negative isolates (Jones and Barry, 1988a; Buck and Price, 1977; Preston et al., 1983). Ceftibuten is more potent and has a broader spectrum of activity than currently available oral cephalosporins, particularly against Citrobacter spp., Enterobacter spp., From the Diagnostic BacteriologyLaboratory, University Hospital St. Rafaelof the University of Leuven, Leuven, Belgium. Address reprint requests to: Dr. L. Verbist, Diagnostic Bacteriology LaboratoryUniversity Hospital St. Rafael of the University of Leuven, Leuven, Belgium. ReceivedMay 25, 1990;revised and accepted July 23, 1990. © 1991Elsevier Science Publishing Co., Inc. 655 Avenue of the Americas, New York, NY 10010 0732-8893/91/$3.50
54
faclor is a first-generation cephalosporin that, like other compounds in its class, is recognized as one of the most active of clinically available cephalosporins against staphylococci and nonenteric streptococci (Donowitz and Mandell, 1988; Moellering and Swartz, 1976; Reynolds, 1989). However, because it is more active against Gram-negative microorganisms than against other agents in its class, cefaclor often is categorized as a second-generation cephalosporin (Reynolds, 1989). Consequently, cefador has become a standard against which new cephalosporins frequently are compared. Cefetamet and cefteram are two esterified cephem antibiotics currently under limited development. Both compounds exhibit greater in vitro activity against microorganisms of the family Enterobacteriaceae than such antimicrobial agents as amoxicillin-clavulanate, ampicillin, cefaclor, cefuroxime, cephalexin, and doxycycline (Chau et al., 1987; Fass and Helsel, 1986; Jones et al., 1986; Verbist, 1987; Wise et al., 1986). Moreover, cefetamet and cefteram demonstrate increased stability to hydrolysis by f3-1actamases, as compared to the early generation cephalosporins, cefaclor, and cephalaxin (Neu et al., 1986). Lastly, tigemonam is a newer orally administered monobactam antibiotic that exhibits a high level of activity, expanded coverage of Gram-negative bacteria, and stability in the presence of various beta-lactamases (Nelet et al., 1990; Tanaka et al., 1987).
MATERIALS AND METHODS Antimicrobial Agents The antibiotics compared in this study included ceftibuten, cefaclor, cefetamet, cefteram, and tigemonam. Other antimicrobial agents used during our research to ensure that multiply-resistant bacteria were obtained for study were amikacin, amoxicillin-clavulanic acid, arnpicillin, cefazolin, cefotaxime, cefuroxime, clindamycin, doxycycline, erythromycin, gentamicin, netilmicin, oxacillin, piperacillin, and tobramycin. All antimicrobial agents were provided by the manufacturers as powders with stated potencies and were prepared as stock solutions.
Microorganisms Bacterial isolates were collected over an 18-month period from - 2 0 hospitals in Belgium. All microorganisms, except those of Streptococcus spp., were tested for resistance to breakpoint concentrations of clinically available antibiotics. Isolates of the family Enterobacteriaceae, Acinetobacter, and Pseudomonas
L. Verbist et al.
spp. were selected for study if resistant to cefazolin, gentamicin, piperacillin, or tobramycin. Strains of Haemophilus influenzae and Neisseria gonorrhoeae usually were chosen if resistant to ampicillin, whereas staphylococci were selected primarily on the basis of resistance to ampicillin or oxacillin. A total of 813 isolates were selected for study: 770 multiply-drug-resistant strains and 43 strains of Streptococcus spp. (Table 1). Among the 770 multiplyresistant microorganisms were Acinetobacter spp. (10 strains), Enterobacteriaceae (641 strains), H. influenzae (35 strains), N. gonorrhoeae (29 strains), Pseudomonas spp. (30 strains), and Staphylococcus spp. (25 strains). Of the 641 enterobacteria, 48% demonstrated resistance to the second-generation cephalosporin, cefuroxime, and 17% were resistant to the third-generation cephem, cefotaxime.
Susceptibility Testing The antimicrobial activity of ceftibuten, cefaclor, cefetamet, cefteram, and tigemonam was tested by an agar dilution method. For most microorganisms, inocula were prepared by dilution of overnight broth cultures in fresh Mueller-Hinton broth, (NCCLS, 1990). Inocula of H. influenzae, N. gonorrhoeae, and Streptococcus spp. (except Enterococcus faecalis) were prepared by dilution in trypticase soy broth following overnight growth on chocolate agar or blood agar. The Mueller-Hinton agar medium was supplemented by 5% lysed horse blood for fastidious microorganisms, in addition to 1% polyvitex for strains of H. influenzae and N. gonorrhoeae. Thereafter, an inoculum of - 5 x 10s colony-forming units (CFU)/spot was delivered by a multipoint inoculator to the agar plates. In general, plates were incubated in ambient air at 36°C for 18 hr. Agar plates containing staphylococci were incubated in ambient air at 34°C for 24 hr and those containing fastidious microorganisms, in 5% CO2 at 36°C for 24 hr. The antimicrobial agents were diluted in distilled water and antibiotic concentrations of 0.015-32 ~xg/mlwere added to the agar plates. The minimum inhibitory concentration (MIC) of the antibiotic was recorded as the lowest concentration of the antimicrobial agent at which bacterial growth was visibly inhibited.
RESULTS Activity Against Microorganisms of the Family Enterobacteriaceae Ceftibuten demonstrated excellent inhibitory activity against most species of multiply-resistant enteric
Ceftibuten Activity in Belgium
TABLE 1.
55
Resistance A m o n g 770 N o n s t r e p t o c o c c a l Clinical Isolates b y Antibiotic a n d M i c r o o r g a n i s m Percent Resistant by Antibiotic (breakpoint in ~g/ml)
Microorganism (no. of isolates)
Acinetobacter spp.
AMI CZL CTX CFU GEN NET PIP TOB ACA AMP CZL CFU CLI DOX ERY OXA (16) (8) (8) (8) (4) (8) (16) (4) (2) (0.25) (2) (2) (0.5) (4) (0.5) (2) 10
70
40
40
40
50
30
30
9
96
35
57
26
22
70
30
10
98
43
77
20
16
51
25
1
34
3
26
12
8
84
16
12 3
80 100
14 13
45 100
58 13
40 5
97 18
54 10
1
69
2
18
22
12
50
10
0
100
0
95
13
3
8
5
2
52
0
36
50
30
70
34
50
100
100
100
100
100 100
80
80
100
80
90
60
90
40
90
30
100
90
100
40
40
30
30
0
43
0
27
43
40
87
43
23
100
80
100
53
81
81
73
0 0
17 100
0 0
3 7
0 0
0 0
28 0
0 0
(10)
Citrobacter spp. (23)
Enterobacter spp. (61)
Escherichia coli (116)
Klebsiella spp. (65) Morganella morganii (40)
Proteus mirabilis (94)
Proteus vulgaris (39)
Providencia spp. (44)
Pseudomonas aeruginosa (10) Xanthomonas maltophilia (10) Pseudomonas spp. (10)
Salmonella spp. (3O)
Serratia marascens (70)
Shigella spp. (29) Yersinia enterocolitica (30) Haemophilus influenzae (35) Neisseria gonorrhoeae (29) Staphylococcus aureus (12) Staphylococcus epidermidis (13)
3
100
69
0
9
0
100
100
0
100
3
0
7
17
3
100
33
100
42
58
17
33
33
42
8
62
8
31
8
23
38
23
AMI, amikacin; ACA, amoxicillin-clavulanic acid; AMP, ampicillin; CZL, cefazolin; CTX, cefotaxime; CFU, cefuroxime; CLI, dindamycin; DOX, doxycycline; ERY, erythromycin; GEN, gentamicin; NET, netilmicin; OXA, oxaciUin; PIP, piperacillin; TOB, tobramycin.
bacilli (Table 2). MICsos w e r e 4 1 ~g/ml for E. coli, Klebsiella s p p . , Proteus mirabilis, P. vulgaris, Providencia s p p . , Salmonella s p p . , Serratia marcescens, Shigella s p p . , a n d Yersinia enterocolitica, a n d the MICso w a s 8 p~g/ml for Morganella morganii. For Citrobacter spp. a n d Enterobacter s p p . , MICsos w e r e > 8 ~g/ml, indicating possible resistance to ceftibuten. Ceftibuten a n d t i g e m o n a m w e r e the m o s t active of the c o m p o u n d s against the Enterobacteriaceae a n d cefaclor w a s the least active. Ceftibuten a n d tige-
m o n a m d e m o n s t r a t e d similar activity against P. mirabilis, P. vulgaris, Providencia, a n d Shigella spp. Ceftibuten w a s m o r e active t h a n t i g e m o n a m against Klebsiella spp. a n d Salmonella spp. T i g e m o n a m w a s m o r e active t h a n ceftibuten against Citrobacter s p p . , Enterobacter s p p . , E. coli, M. morganii, S. marcescens, a n d Y. enterocolitica. C e f e t a m e t a n d cefteram w e r e similar in activity against Citrobacter s p p . , Enterobacter s p p . , Salmonella s p p . , a n d Shigella s p p . , as well as P. vulgaris a n d S. marcescens. C e f e t a m e t w a s m o r e
56
L. Verbist et al.
TABLE 2.
In vitro Antimicrobial Activity of Ceftibuten, Cefaclor, Cefetamet, Cefteram a n d T i g e m o n a m Against 813 Clinical Isolates MIC (~g/ml)
Microorganism (no. of isolates) Citrobacter spp. (23)
Antibiotic
Range
50%
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.12->32 8-> 128 1->32 0.5-> 32 0.12->32
32 64 8 32 1
Enterobacter spp. ( 6 1 )
Ceftibuten Cefaclor Cefetarnet Cefteram Tigemonam
0.03->32 16->128 0.25->32 0.12->32 0.06->32
>32 >128 >32 32 1
E. coli (116)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.015->32 0.5-> 128 0.12->32 0.06-> 32 0.015->32
Klebsiella spp. (65)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
M. morganii (40)
90%
>32 >32 32
8.23 64.00 10.49 11.84 1.30
>32 >128 >32 >32 16
10.26 >128 15.46 12.20 1.26
0.25 4 1 0.5 0.25
16 128 32 4 1
0.61 8.24 2.32 0.87 0.33
0.015->32 0.25-> 128 0.12->32 0.25-> 32 0.015-32
0.06 16 0.5 2 0.5
1 > 128 4 > 32 16
0.12 23.74 0.78 2.40 1.11
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.03->32 64-> 128 4->32 0.12->32 0.015-16
8 > 128 >32 16 0.25
>32 > 128 >32 >32 2
2.71 > 128 >32 8.09 0.26
P. mirabilis (94)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.015-16 0.5-> 128 0.06->32 0.015-> 32 0.015-16
0.015 8 0.12 0.12 0.015
0.06 > 128 2 0.5 0.12
0.03 8.42 0.27 0.13 0.03
P. vulgaris (39)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.015-8 4->128 0.12->32 0.12-32 0.015-0.25
0.015 128 0.25 0.25 0.015
0.03 >128 1 2 0.03
0.03 >128 0.37 0.32 0.02
Providencia spp. (44)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.015-16 1- > 128 0.03->32 0.03->32 0.015-1
0.015 64 0.25 0.5 0.015
0.06 > 128 4 8 0.06
0.02 55.54 0.25 0.55 0.02
Salmonella spp. (30)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.03->32 0.5-64 0.25->32 0.25-> 32 0.12-> 32
0.06 2 0.5 0.5 0.25
0.12 16 2 1 0.5
0.09 3.73 0.91 0.78 0.44
S. marcescens (70)
Ceftibuten Cefaclor Cefetamet Cefteram
0.12-32 > 128 1->32 2->32
1 > 128 8 8
>32
Geometric Mean
> 128
8 > 128 >32 >32
1.12 > 128 10.56 13.52
Ceftibuten Activity in Belgium
TABLE 2.
57
Continued MIC (p.g/ml)
Microorganism (no. of isolates)
Geometric Mean
Range
50%
Tigemonam
0.12-16
0.5
1
0.57
Shigella spp. (29)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.03--0.25 0.5-32 0.03-1 0.03-4 0.03-0.25
0.12 2 0.12 0.12 0.06
0.25 8 0.5 0.25 0.25
0.11 1.50 0.15 0.28 0.08
Y. enterocolitica (30)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.06-8 8->128 0.5-32 0.25--4 0.06-0.12
0.12 16 0.5 0.5 0.06
4 > 128 32 2 0.12
0.25 22.63 1.45 0.47 0.08
Acinetobacter spp.
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
(10)
Antibiotic
0.03->32 0.25->32 0.03->32 0.03->32 0.015->32
90%
32 32 4 8 2
32 >32 >32 >32 32
6.00 27.90 2.60 5.60 3.50
P. aeruginosa (10)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
>32 >32 >32 >32 >32
>32 >32 >32 >32 >32
>32 >32 >32 >32 >32
>32 >32 >32 >32 >32
X. maltophilia (10)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.5->32 8->32 2->32 4->32 1->32
32 >32 >32 >32 32
>32 >32 >32 >32 >32
14.90 >32 26.00 >32.00 19.70
Pseudomonas spp.
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
2->32 >32 8->32 16->32 1->32
>32 >32 >32 >32 >32
>32 >32 >32 >32 >32
>32 >32 >32 >32 27.90
H. influenzae (35)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.015-0.03 1-4 0.06-0.25 0.015 0.015-0.25
0.03 1 0.25 0.015 0.06
0.03 2 0.25 0.015 0.12
0.03 1.43 0.21 0.02 0.08
N. gonorrhoeae (29)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.015-0.12 0.12-2 0.015-0.5 0.015-0.12 0.015-0.12
0.015 0.12 0.015 0.015 0.015
0.015 1 0.03 0.015 0.03
0.02 0.16 0.02 0.02 0.02
Staphylococcus aureus
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
32->32 0.6->32 16->32 2->32 16->32
>32 8 >32 8 32
>32 32 >32 >32 32
>32 6.70 >32 10.70 30.20
8->32 0.25-32 8->32 1->32
32 4 32 4
>32 16 >32 >32
30.20 2.30 28.80 6.50
(10)
(12)
S. epidermidis (13)
Ceftibuten Cefaclor Cefetamet Cefteram
L. Verbist et al.
58
TABLE 2.
Continued MIC (~g/ml)
Microorganism (no. of isolates)
Streptococcus agalactiae (11)
Antibiotic
Range
50%
90%
Geometric Mean
Tigemonam
4-32
32
32
24.50
16
32
19.30
1
4
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
16-32 1-4 4-16 0.03-1 32->32
S. pneumoniae (12)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
1-2 0.12-0.25 0.25-0.5 0.015 2-8
2 0.25 0.25 0.015 4
2 0.25 0.6 0.015 8
1.78 0.22 0.35 0.02 4.76
S. pyogenes (10)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.5 0.12-0.25 0.06 0.015-0.06 1
0.5 0.25 0.06 0.015 1
0.5 0.25 0.06 0.015 1
0.50 0.19 0.06 0.02 1.00
Enterococcus (10)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
>32 32->32 >32 >32 32->32
active than cefteram against Klebsiella spp. and Providencia spp. Cefteram, in turn, demonstrated greater activity than cefetamet against E. coli, M. morganii, P. mirabilis, and Y. enterocolitica. To assess the overall antimicrobial activity of these agents, we calculated geometric mean MICs of each antibiotic for the Enterobacteriaceae. Overall activity was comparable for ceftibuten and tigemonam (geometric mean MIC = 0.30 g,g/ml and 0.20 p~g/ml, respectively), but was about 4-9 times greater than that of cefetamet and cefteram (geometric mean MIC = 1.72 ~,g/ml and 1.24 ~g/ml, respectively). Cefetamet and cefteram demonstrated similar overall activity. The activity of cefador was comparatively poor (geometric mean MIC = 30.19 ~g/ml). Ceftibuten at a concentration of 48 ~g/ml inhibited 85% of multiply-resistant enterobacteria. For the most part, this level of antimicrobial activity was superior to that observed with the comparative compounds. Only 37% of these enteric bacilli were susceptible to cefaclor (48 ~g/ml), 69% to cefetamet (44 ~g/ml), 59% to cefteram (41 ~g/ml), and 95% to tigemonam (48 ~g/ml). Susceptible breakpoints used were those defined by the NCCLS for compounds closely related to ceftibuten, cefetamet, cefteram, and tigemonam, that is, cefaclor, cefuroxime axetil, ce-
8 0.06 32
>32 >32 >32 >32 >32
16 0.5 32
>32 >32 >32 >32 >32
1.46
7.51 0.09 >32
>32 >32 >32 >32 >32
fixime, and aztreonam. The percentages of enterobacteria that were susceptible to other alternative breakpoint concentrations of 42, 4, and 8 ~g/ml are compared in Table 3. The susceptibility of cefuroxime- and cefotaximeresistant strains of Enterobacteriaceae to ceftibuten, cefetamet, cefteram, and tigemonam was determined. The findings are presented in Table 4. Cefuroxime-susceptible strains were most susceptible to the new oral [3-1actam compounds, as compared to cefuroxime- and cefotaxime-resistant strains. Susceptibility to ceftibuten, cefetamet, cefteram, and tigemonam decreased slightly among those strains that were resistant to cefuroxime, but susceptible to cefotaxime. Susceptibility decreased fiLrther among the cefotaxime-resistant bacteria. This decrease in activity occurred with all four antibiotics, but not to the same extent. Based on the ratio of the geometric mean MIC for cefotaxime-resistant strains to the geometric mean MIC for cefuroxime-susceptible strains, activity decreased -60-100 times with ceftibuten, cefetamet, and cefteram; a 20-fold decrease was observed with tigemonam. These results may suggest that tigemonam is less affected by some resistance mechanisms (f~-lactamases or permeability mutations) than ceftibuten, cefetamet, or cefteram.
59
Ceftibuten Activity in Belgium
TABLE 3.
Susceptibility of 813 Clinical Isolates to Ceftibuten, Cefaclor, Cefetamet, Cefteram, a n d T i g e m o n a m at Concentrations of 4 2 , 4 4 , a n d 4 8 ~g/ml % Susceptible to Concentration of Antibiotic in ~g/ml Ceftibuten
Cefaclor
Cefetamet
Cefteram
Tigemonam
Microorganism (no. of isolates)
42
44
48
42
~4
48
42
44
48
~2
~4
~8
42
44
48
Enterobacteriaceae
77
80
85
19
28
37
64
69
75
68
74
79
90
93
95
40
40
40
20
20
20
0
50
70
30
40
40
50
50
50
13
13
13
0
0
0
7
7
13
0
3
7
13
13
17
100 100 0
100 100 0
100 100 8
97 100 36
100 100 52
100 100 76
100 100 0
100 100 0
100 100 12
100 100 24
100 100 44
100 100 68
100 100 0
100 100 0
100 100 8
51
51
51
72
77
77
51
58
72
77
77
77
30
37
51
(641)
Acinetobacter spp. (lO)
Pseudomonas spp. ~ (30)
H. influenzae (35) N. gonorrhoeae (29) Staphylococcus spp. (25)
Streptococcus spp. (43)
qncludes X. maltophilia;
Activity Against H. influenzae and N.
lower than those specified by the N C C L S breakpoints for similar c o m p o u n d s (NCCLS, 1990).
gonorrhoeae Ceftibuten, cefetamet, cefteram, and tigemonam were very active against strains of H. influenzae a n d N. gonorrhoeae. To exemplify, the MIC9o of ceftibuten was 4 0 . 0 3 ~g/ml for b o t h of these species. Cefaclor w a s less active t h a n the comparative c o m p o u n d s against these species. As is evident in Tables 2 a n d 3, 100% of strains of b o t h species were susceptible to each of the c o m p o u n d s at concentrations that were TABLE 4.
Activity Against Staphylococcus and
Streptococcus s p p .
Staphylococci were almost completely resistant to the n e w beta-lactam c o m p o u n d s . The MICs0s for strains of Staphylococcus aureus a n d Staphylococcus epidermidis were in the resistant range for ceftibuten, cefetamet, cefteram, a n d t i g e m o n a m . Cefaclor was
Susceptibility of Enterobacteriaceae to Ceftibuten, Cefetamet, Cefteram, a n d T i g e m o n a m Categorized b y their Susceptibility/Resistance to Cefuroxime a n d Cefotaxime Cumulative Percentage of Strains Inhibited by Concentration of Antibiotic in ~g/ml
Strain (no. of isolates)
Antibiotic
0.015 0.03 0.06 0.12 0.25 0.5
1
2
4
8
96 92 97 98
98 94 98 99
99.1 97 99 99.1
Cefuroxime-susceptible a Ceftibuten (334) Cefetamet Cefteram Tigemonam
28 -2 26
42 3 5 32
53 11 17 44
74 29 32 57
86 44 55 87
90 94 68 84 76 89 95 97
Cefuroxime-resistantb (198)
Ceftibuten Cefetamet Cefteram Tigemonam
17 --18
31 --30
37 -3 38
44 6 15 43
53 19 22 58
Cefotaxime-resistant~ (109)
Ceftibuten Cefetamet Cefteram Tigemonam
-. . --
-. . --
3
15
. . 1
17
-. .
. . --
~Strains susceptible to cefuroxime 48 ~g/ml. bStrains resistant to cefuroxime, but susceptible to cefotaxime ~8 ~g/rnl. cStrains resistant to cefotaxime.
16
32
Geometric Mean MIC
9 9 . 1 99.1 99 100 99 99.7 99.1 99.7
0.08 0.43 0.31 0.10
60 64 69 71 78 27 38 50 57 63 29 40 56 67 75 74 85 90 94 97
90 70 83 98
91 76 94 99
0.48 3.86 2.24 0.21
25 30 37 1 2 6 1 1 4 31 51 64
56 33 27 93
65 43 38 98
6.74 25.13 30.80 1.88
42 19 12 74
52 30 24 79
60
the most active of the agents evaluated against staphylococci and inhibited 58% and 92% of strains of S. aureus and S. epidermidis, respectively. Table 3 shows the low percentage of staphylococci, in general, inhibited by concentrations of ~2, 4, and 8 p~g/ml. Against streptococci, cefteram was the most active and tigemonam the least active of the antimicrobial agents tested (Table 2). Ceftibuten was highly active against strains of Streptococcus pyogenes; the MIC9o was 0.5 p,g/ml. Against Streptococcus pneumoniae, the MIC90 of ceftibuten was 2 p~g/ml. Strains of Streptococcus agalactiae (serogroup B) were uniformly resistant to inhibition by ceftibuten and tigemonam, and most strains of this species were resistant to cefetamet, as well. Cefteram exhibited the greatest inhibitory activity against this species (MIC90 = 0.5 ~g/ml), as compared to cefaclor (MIC90 = 4 p~g/ml). Strains of E. faecalis were consistently resistant to all of the antibiotics tested. The percentages of streptococci that were susceptible to each of the compounds at various breakpoints are shown in Table 3.
Activity Against Other Microorganisms Isolates of Pseudomonas aeruginosa were uniformly resistant to all of the compounds evaluated. Against strains of Pseudomonas maltophilia, other Pseudomonas spp. and Acinetobacter spp., the activity of all agents was minimal and limited to inhibition of a few unusually susceptible isolates, particularly among the Acinetobacter spp. DISCUSSION It has long been recognized that bacteria are especially adept at developing resistance to antibiotics (Neu, 1984). In fact, resistant microorganisms appear to arise as quickly as new antimicrobial agents are introduced (Lafong and Murphy, 1986). Thus, intensive research continues in an effort to develop antibiotics that will inhibit multiply-drug-resistant pathogens. Ceftibuten is a new, nonesterified, orally active cephem antibiotic with excellent pharmacokinetic properties (Nakashima et al., 1988) and potent activity against a wide range of Gram-negative and
L. Verbist et al.
selected Gram-positive bacteria (Hamashima et al., 1987; Jones and Barry, 1988a). In this present study, we compared the in vitro activity of ceftibuten with that of other orally active ~-lactam compounds: cefaclor, a first-generation cephalosporin; cefetamet and cefteram, two esterified cephems currently under evaluation; and tigemonam, a recently investigated monobactam. Ceftibuten, cefetamet, cefteram, and tigemonam were much more active than cefaclor against multiply-resistant Enterobacteriaceae, and ceftibuten and tigemonam were the most active of the agents tested. Also, all of the new agents exhibited excellent activity against multiply-resistant strains of H. influenzae and N. gonorrhoeae and were somewhat more active than cefaclor against these species. Against staphylococcal isolates, cefaclor was far more active than any of the comparative compounds. Moreover, the new [3-1actam agents generally exhibited no better activity than cefaclor against streptococcal strains, except for cefteram. Strains of E. faecalis and P. aeruginosa were consistently resistant to inhibition by all of the agents evaluated, and none of the compounds had any useful activity against isolates of other Pseudomonas spp. or Acinetobacter spp. Our study of the comparative in vitro activity of ceftibuten confirms the findings of other researchers (Jones and Barry, 1988a-d; Shawar et al., 1989). Ceftibuten has potent activity against many members of the Enterobacteriaceae, H. influenzae, N. gonorrhoeae, and S. pyogenes, and many of these microorganisms demonstrate resistance to multiple antibiotics (Jones and Barry, 1988a--d; Shawar et al., 1989). Ceftibuten also has proven to be highly active against strains of Moraxella (Branhamella) catarrhalis, and Neisseria meningitidis in other studies (jones and Barry, 1988a-c). Based on these data, ceftibuten may be indicated in the treatment of patients with urinary tract infections caused by most Enterobacteriaceae, genital infections caused by pathogenic Neisseria spp. and lower and upper respiratory tract infections caused by such organisms as H. influenzae, M. catarrhalis, most pneumococci, and B-hemolytic streptococci.
This study was supported by a grant from Schering Corporation and a grant from E.R. Squibb and Sons.
Ceftibuten Activity in Belgium
61
REFERENCES Buck RE, Price KE (1977) Cefadroxil, a new broad-spectrum cephalosporin. Antimicrob Agents Chemother 11:324330. Chau PY, Leung YK, NG WW, Arnold K (1987) Comparative in vitro antibacterial activities of two new oral cephalosporins, ceftetrame (Ro 19-5247) and cefetamet (Ro 15-8074). Antimicrob Agents Chemother 31:473-476. Donowitz GR, Mandell GL (1988) Beta-lactam antibiotics. N Engl J Med 318:490-500. Fass RJ, Helsel VL (1986) In vitro activities of Ro 19-5247 and Ro-15-8074, new oral cephalosporins. Antimicrob Agents Chemother 30:429-434. Fuchs PC, Barry AL, Jones RN (1986) Cefixime disk susceptibility test criteria. J Clin Microbiol 24:647-649. Guay DR, Meatherall RC, Harding GK, Brown GR (1986) Pharmacokinetics of cefixime (CL 284,635; FK 027) in healthy subjects and patients with renal insufficiency. Antimicrob Agents Chemother 30:483-490. Hamashima Y, Kubota T, Minami K, Ishikura K, Konoike T, Yoshioka M, Yoshida T, Nakashimizu H, Motokawa K (1987) Synthesis and biological properties of 7 beta[(Z)2-(2-amino-4-thiazolyl)-4-carboxy-2-butenoylamino]-3cephem-4-carboxylic acid (7432-S), a new oral cephem antibiotic. J Antibiotics 40:1468-1470. Jones RN, Barry AL (1988a) Antimicrobial activity, spectrum, and recommendations for disk diffusion susceptibility testing of ceftibuten (7432-S; SCH 39720), a new orally administered cephalosporin. Antimicrob Agents Chemother 32:1576-1582. Jones RN, Barry AL (1988b) In-vitro antimicrobial activity of 7432-S (SCH 39720) against commonly isolated respiratory tract pathogens. J Antimicrob Chemother 22:387389. Jones RN, Barry AL (1988c) In vitro evaluation of ceftibuten (7432-S, SCH 39720), a novel orally administered cephalosporin. Chemioterapia 7:283-286. Jones RN, Barry AL, The Collaborative Antimicrobial Susceptibility Testing Group (1988) Ceftibuten (7432-S, SCH 39720): comparative antimicrobial activity against 4735 clinical isolates, beta-lactamase stability and broth microdilution quality control guidelines. Eur J Clin Microbiol Infect Dis 7:802-807. Jones RN, Fuchs PC, Barry AL, Ayers LW, Gerlach EH, Gavan TL (1986) Antimicrobial activity of Ro-8074, active metabolite of a new oral cephalosporin (Ro 158075), against 7,775 recent clinical isolates. Antimicrob Agents Chemother 30:961-963. Lafong AC, Murphy PG (1986) New antibacterial agents and their uses. J Clin Hosp Pharm 11:237-269.
Moellering RC Jr, Swartz MN (1976) The newer cephalosporins. N Engl J Med 294:24-28. Nakashima M, Uematsu T, Takiguchi Y, Mizuno A, Iida M, Yoshida T, Yamamoto S, Kitagawa K, Oguma T, Ishii H, Yamada H (1988) Phase I clinical studies of 7432-S, a new oral cephalosporin: safety and pharmacokinetics. J Clin Pharmacol 28:246-252. National Committee for Clinical Laboratory Standards (NCCLS) (1990) Approved standard M7-A2. Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically. Villanova, PA: NCCLS. Nelet F, Gutmann L, Kitzis MD, Acar JF (1989) Tigemonam activity against clinical isolates of Enterobacteriaceae and Enterobacteriaceae with known mechanisms of resistance to beta-lactam antibiotics. J Antimicrob Chemother 24:173-181. Neu H (1984) Changing mechanisms of bacterial resistance. Am J Med 77:1-23. Neu HC, Chin N-X, Labthavikul P (1986) In vitro activity and beta-lactamase stability of two oral cephalosporins, ceftetrame (Ro 19-5247) and cefetamet (Ro 15-8074). Antimicrob Agents Chemother 30:423-428. Preston DA, Jones RN, Barry AL, Thornsberry C (1983) Comparison of the antibacterial spectra of cephalexin and cefaclor with those of cephalothin and newer cephalosporins: Reevaluation of the class representative concept of susceptibility testing. J Clin Microbiol 17:11561158. Reynolds JE, Ed. (1989) Antibacterial agents. In Martindale the Extra Pharmacopoeia. London: Pharmaceutical Press, p 105. Shawar R, LaRocco M, Cleary TG (1989) Comparative in vitro activity of ceffibuten (SCH 39720) against bacterial enteropathogens. Antimicrob Agents Chemother 33:781784. Shimada J, Saito A, Shimada K (1986) T-2588, a thirdgeneration oral cephalosporin: human pharmacokinetics. In Recent Advances in Chemotherapy. Ed, J Ishigami. Tokyo: University of Tokyo Press, pp 1179-1180. Tanaka S Ken, Summerill RA Schwind, Minassian BF, Bush K, Visnic DA, Bonner DP, Sykes RB (1987) In vitro evaluation of tigemonam, a novel oral monobactam. Antimicrob Agents Chemother 31:219-225. Verbist L (1987) Comparative in vitro activity of Ro 158074 and Ro 19-5247, two new oral cephalosporins, against resistant organisms. FAC Fortschr Antimikr Antineoplast Chemother 6:1267-1272. Wise R, Andrews JM, Piddock LJ (1986) In vitro activity of Ro 15-8074 and Ro 19-5247, two orally administered cephalosporin metabolites. Antimicrob Agents Chemother 29:1067-1072.
53
Comparative Antimicrobial Activity of Ceftibuten Against Multiply-Resistant Microorganisms from Belgium Ludo Verbist, Jan Jacobs, and Koen Hens
To study the activity of ceftibuten, we obtained multiply-resistant isolates from -20 hospitals in Belgium. Against Enterobacteriaceae, all of the tested comparative compounds were more active than cefaclor, and ceftibuten and tigemonam were the most active of the agents tested. Ceftibuten MICsos were 41 i~g/ml for most enteric bacilli species and 85% of strains were susceptible (48 i~g/ml). This level of activity compared favorably to that recorded for cefaclor (48 I~g/ml), cefetamet (44 I~g/ml), and cefteram (41 i~g/ml), that is, 37%, 69%, and 59%, respectively. Ceftibuten, cefetamet, cefteram, and tigemonam were highly active against isolates 0f Haemophilus influenzae and Neisseria gonorrhoeae. None of the comparative agents were as ac-
tive as cefaclor against staphylococcal isolates. Against streptococci, cefleram was the most active, and tigemonam the least active of the agents. The MICgos of ceftibuten for strains of Streptococcus pneumoniae and Streptococcus pyogenes were 2 i~g/ml and 0.5 i~g/ml, respectively. Strains of Streptococcus agalactiae were resistant to both ceflibuten and tigemonam; cefaclor and cefleram inhibited 100% of isolates of this species. Strains 0f Enterococcus faecalis and Pseudomonas aeruginosa were consistently resistant to all of the compounds. Overall, ceftibuten exhibited potent activity against many multiply-resistant clinical isolates.
INTRODUCTION
Escherichia coli, Haemophilus influenzae, Klebsiella spp., Morganella morganii, Proteus spp., Providencia spp., and Serratia spp. (Hamashima et al., 1987; Jones and Barry, 1988a, c, and d). Some investigational, orally absorbed, third-generation cephems, such as cefixime and cefteram, exhibit antimicrobial activity similar to that of ceftibuten (Chau et al., 1987; Fass and Helsel, 1986; Jones and Barry, 1988a and d; N e u et al., 1986; Wise et al., 1986). However, ceftibuten is absorbed especially well, resulting in better drug bioavailability than that attained with comparative compounds (Fuchs et al., 1986; Guay et al., 1986; Nakashima et al., 1988; Shimada et al., 1986). A single 200-mg dose given to volunteers provides mean maximum plasma concentrations of 11.6 ~g/ml and has a half-life of - 1 . 9 hr (Nakashima et al., 1988); -65% of therapeutic concentrations of ceftibuten are bound to serum proteins (Nakashima et al., 1988). Ceftibuten is stable to degradation by certain [~-lactamases, including those that can hydrolyze such early-generation cephalosporins as cefaclor and cephaloridine (Jones and Barry, 1988d). A study was undertaken to compare the in vitro activity of ceftibuten with that of other orally absorbed ~-lactam antibiotics, namely, cefaclor, cefetamet, cefteram, and tigemonam. In particular, ce-
Ceftibuten is a novel, orally administered cephalosporin. Unlike such investigational oral cephems as cefetamet and cefteram, gastrointestinal absorption of ceftibuten is achieved without inclusion of an ester in this agent's chemical structure (Hamashima et al., 1987; Shimada et al., 1986; Wise et al., 1986). This structural difference has proven to be advantageous over other nonesterified, orally absorbed cephalosporins, such as cephadroxil, cefaclor, cefixime, and BMY-28100, by demonstrating either enhanced pharmacokinetics or potency against certain Gram-negative isolates (Jones and Barry, 1988a; Buck and Price, 1977; Preston et al., 1983). Ceftibuten is more potent and has a broader spectrum of activity than currently available oral cephalosporins, particularly against Citrobacter spp., Enterobacter spp., From the Diagnostic BacteriologyLaboratory, University Hospital St. Rafaelof the University of Leuven, Leuven, Belgium. Address reprint requests to: Dr. L. Verbist, Diagnostic Bacteriology LaboratoryUniversity Hospital St. Rafael of the University of Leuven, Leuven, Belgium. ReceivedMay 25, 1990;revised and accepted July 23, 1990. © 1991Elsevier Science Publishing Co., Inc. 655 Avenue of the Americas, New York, NY 10010 0732-8893/91/$3.50
54
faclor is a first-generation cephalosporin that, like other compounds in its class, is recognized as one of the most active of clinically available cephalosporins against staphylococci and nonenteric streptococci (Donowitz and Mandell, 1988; Moellering and Swartz, 1976; Reynolds, 1989). However, because it is more active against Gram-negative microorganisms than against other agents in its class, cefaclor often is categorized as a second-generation cephalosporin (Reynolds, 1989). Consequently, cefador has become a standard against which new cephalosporins frequently are compared. Cefetamet and cefteram are two esterified cephem antibiotics currently under limited development. Both compounds exhibit greater in vitro activity against microorganisms of the family Enterobacteriaceae than such antimicrobial agents as amoxicillin-clavulanate, ampicillin, cefaclor, cefuroxime, cephalexin, and doxycycline (Chau et al., 1987; Fass and Helsel, 1986; Jones et al., 1986; Verbist, 1987; Wise et al., 1986). Moreover, cefetamet and cefteram demonstrate increased stability to hydrolysis by f3-1actamases, as compared to the early generation cephalosporins, cefaclor, and cephalaxin (Neu et al., 1986). Lastly, tigemonam is a newer orally administered monobactam antibiotic that exhibits a high level of activity, expanded coverage of Gram-negative bacteria, and stability in the presence of various beta-lactamases (Nelet et al., 1990; Tanaka et al., 1987).
MATERIALS AND METHODS Antimicrobial Agents The antibiotics compared in this study included ceftibuten, cefaclor, cefetamet, cefteram, and tigemonam. Other antimicrobial agents used during our research to ensure that multiply-resistant bacteria were obtained for study were amikacin, amoxicillin-clavulanic acid, arnpicillin, cefazolin, cefotaxime, cefuroxime, clindamycin, doxycycline, erythromycin, gentamicin, netilmicin, oxacillin, piperacillin, and tobramycin. All antimicrobial agents were provided by the manufacturers as powders with stated potencies and were prepared as stock solutions.
Microorganisms Bacterial isolates were collected over an 18-month period from - 2 0 hospitals in Belgium. All microorganisms, except those of Streptococcus spp., were tested for resistance to breakpoint concentrations of clinically available antibiotics. Isolates of the family Enterobacteriaceae, Acinetobacter, and Pseudomonas
L. Verbist et al.
spp. were selected for study if resistant to cefazolin, gentamicin, piperacillin, or tobramycin. Strains of Haemophilus influenzae and Neisseria gonorrhoeae usually were chosen if resistant to ampicillin, whereas staphylococci were selected primarily on the basis of resistance to ampicillin or oxacillin. A total of 813 isolates were selected for study: 770 multiply-drug-resistant strains and 43 strains of Streptococcus spp. (Table 1). Among the 770 multiplyresistant microorganisms were Acinetobacter spp. (10 strains), Enterobacteriaceae (641 strains), H. influenzae (35 strains), N. gonorrhoeae (29 strains), Pseudomonas spp. (30 strains), and Staphylococcus spp. (25 strains). Of the 641 enterobacteria, 48% demonstrated resistance to the second-generation cephalosporin, cefuroxime, and 17% were resistant to the third-generation cephem, cefotaxime.
Susceptibility Testing The antimicrobial activity of ceftibuten, cefaclor, cefetamet, cefteram, and tigemonam was tested by an agar dilution method. For most microorganisms, inocula were prepared by dilution of overnight broth cultures in fresh Mueller-Hinton broth, (NCCLS, 1990). Inocula of H. influenzae, N. gonorrhoeae, and Streptococcus spp. (except Enterococcus faecalis) were prepared by dilution in trypticase soy broth following overnight growth on chocolate agar or blood agar. The Mueller-Hinton agar medium was supplemented by 5% lysed horse blood for fastidious microorganisms, in addition to 1% polyvitex for strains of H. influenzae and N. gonorrhoeae. Thereafter, an inoculum of - 5 x 10s colony-forming units (CFU)/spot was delivered by a multipoint inoculator to the agar plates. In general, plates were incubated in ambient air at 36°C for 18 hr. Agar plates containing staphylococci were incubated in ambient air at 34°C for 24 hr and those containing fastidious microorganisms, in 5% CO2 at 36°C for 24 hr. The antimicrobial agents were diluted in distilled water and antibiotic concentrations of 0.015-32 ~xg/mlwere added to the agar plates. The minimum inhibitory concentration (MIC) of the antibiotic was recorded as the lowest concentration of the antimicrobial agent at which bacterial growth was visibly inhibited.
RESULTS Activity Against Microorganisms of the Family Enterobacteriaceae Ceftibuten demonstrated excellent inhibitory activity against most species of multiply-resistant enteric
Ceftibuten Activity in Belgium
TABLE 1.
55
Resistance A m o n g 770 N o n s t r e p t o c o c c a l Clinical Isolates b y Antibiotic a n d M i c r o o r g a n i s m Percent Resistant by Antibiotic (breakpoint in ~g/ml)
Microorganism (no. of isolates)
Acinetobacter spp.
AMI CZL CTX CFU GEN NET PIP TOB ACA AMP CZL CFU CLI DOX ERY OXA (16) (8) (8) (8) (4) (8) (16) (4) (2) (0.25) (2) (2) (0.5) (4) (0.5) (2) 10
70
40
40
40
50
30
30
9
96
35
57
26
22
70
30
10
98
43
77
20
16
51
25
1
34
3
26
12
8
84
16
12 3
80 100
14 13
45 100
58 13
40 5
97 18
54 10
1
69
2
18
22
12
50
10
0
100
0
95
13
3
8
5
2
52
0
36
50
30
70
34
50
100
100
100
100
100 100
80
80
100
80
90
60
90
40
90
30
100
90
100
40
40
30
30
0
43
0
27
43
40
87
43
23
100
80
100
53
81
81
73
0 0
17 100
0 0
3 7
0 0
0 0
28 0
0 0
(10)
Citrobacter spp. (23)
Enterobacter spp. (61)
Escherichia coli (116)
Klebsiella spp. (65) Morganella morganii (40)
Proteus mirabilis (94)
Proteus vulgaris (39)
Providencia spp. (44)
Pseudomonas aeruginosa (10) Xanthomonas maltophilia (10) Pseudomonas spp. (10)
Salmonella spp. (3O)
Serratia marascens (70)
Shigella spp. (29) Yersinia enterocolitica (30) Haemophilus influenzae (35) Neisseria gonorrhoeae (29) Staphylococcus aureus (12) Staphylococcus epidermidis (13)
3
100
69
0
9
0
100
100
0
100
3
0
7
17
3
100
33
100
42
58
17
33
33
42
8
62
8
31
8
23
38
23
AMI, amikacin; ACA, amoxicillin-clavulanic acid; AMP, ampicillin; CZL, cefazolin; CTX, cefotaxime; CFU, cefuroxime; CLI, dindamycin; DOX, doxycycline; ERY, erythromycin; GEN, gentamicin; NET, netilmicin; OXA, oxaciUin; PIP, piperacillin; TOB, tobramycin.
bacilli (Table 2). MICsos w e r e 4 1 ~g/ml for E. coli, Klebsiella s p p . , Proteus mirabilis, P. vulgaris, Providencia s p p . , Salmonella s p p . , Serratia marcescens, Shigella s p p . , a n d Yersinia enterocolitica, a n d the MICso w a s 8 p~g/ml for Morganella morganii. For Citrobacter spp. a n d Enterobacter s p p . , MICsos w e r e > 8 ~g/ml, indicating possible resistance to ceftibuten. Ceftibuten a n d t i g e m o n a m w e r e the m o s t active of the c o m p o u n d s against the Enterobacteriaceae a n d cefaclor w a s the least active. Ceftibuten a n d tige-
m o n a m d e m o n s t r a t e d similar activity against P. mirabilis, P. vulgaris, Providencia, a n d Shigella spp. Ceftibuten w a s m o r e active t h a n t i g e m o n a m against Klebsiella spp. a n d Salmonella spp. T i g e m o n a m w a s m o r e active t h a n ceftibuten against Citrobacter s p p . , Enterobacter s p p . , E. coli, M. morganii, S. marcescens, a n d Y. enterocolitica. C e f e t a m e t a n d cefteram w e r e similar in activity against Citrobacter s p p . , Enterobacter s p p . , Salmonella s p p . , a n d Shigella s p p . , as well as P. vulgaris a n d S. marcescens. C e f e t a m e t w a s m o r e
56
L. Verbist et al.
TABLE 2.
In vitro Antimicrobial Activity of Ceftibuten, Cefaclor, Cefetamet, Cefteram a n d T i g e m o n a m Against 813 Clinical Isolates MIC (~g/ml)
Microorganism (no. of isolates) Citrobacter spp. (23)
Antibiotic
Range
50%
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.12->32 8-> 128 1->32 0.5-> 32 0.12->32
32 64 8 32 1
Enterobacter spp. ( 6 1 )
Ceftibuten Cefaclor Cefetarnet Cefteram Tigemonam
0.03->32 16->128 0.25->32 0.12->32 0.06->32
>32 >128 >32 32 1
E. coli (116)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.015->32 0.5-> 128 0.12->32 0.06-> 32 0.015->32
Klebsiella spp. (65)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
M. morganii (40)
90%
>32 >32 32
8.23 64.00 10.49 11.84 1.30
>32 >128 >32 >32 16
10.26 >128 15.46 12.20 1.26
0.25 4 1 0.5 0.25
16 128 32 4 1
0.61 8.24 2.32 0.87 0.33
0.015->32 0.25-> 128 0.12->32 0.25-> 32 0.015-32
0.06 16 0.5 2 0.5
1 > 128 4 > 32 16
0.12 23.74 0.78 2.40 1.11
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.03->32 64-> 128 4->32 0.12->32 0.015-16
8 > 128 >32 16 0.25
>32 > 128 >32 >32 2
2.71 > 128 >32 8.09 0.26
P. mirabilis (94)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.015-16 0.5-> 128 0.06->32 0.015-> 32 0.015-16
0.015 8 0.12 0.12 0.015
0.06 > 128 2 0.5 0.12
0.03 8.42 0.27 0.13 0.03
P. vulgaris (39)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.015-8 4->128 0.12->32 0.12-32 0.015-0.25
0.015 128 0.25 0.25 0.015
0.03 >128 1 2 0.03
0.03 >128 0.37 0.32 0.02
Providencia spp. (44)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.015-16 1- > 128 0.03->32 0.03->32 0.015-1
0.015 64 0.25 0.5 0.015
0.06 > 128 4 8 0.06
0.02 55.54 0.25 0.55 0.02
Salmonella spp. (30)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.03->32 0.5-64 0.25->32 0.25-> 32 0.12-> 32
0.06 2 0.5 0.5 0.25
0.12 16 2 1 0.5
0.09 3.73 0.91 0.78 0.44
S. marcescens (70)
Ceftibuten Cefaclor Cefetamet Cefteram
0.12-32 > 128 1->32 2->32
1 > 128 8 8
>32
Geometric Mean
> 128
8 > 128 >32 >32
1.12 > 128 10.56 13.52
Ceftibuten Activity in Belgium
TABLE 2.
57
Continued MIC (p.g/ml)
Microorganism (no. of isolates)
Geometric Mean
Range
50%
Tigemonam
0.12-16
0.5
1
0.57
Shigella spp. (29)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.03--0.25 0.5-32 0.03-1 0.03-4 0.03-0.25
0.12 2 0.12 0.12 0.06
0.25 8 0.5 0.25 0.25
0.11 1.50 0.15 0.28 0.08
Y. enterocolitica (30)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.06-8 8->128 0.5-32 0.25--4 0.06-0.12
0.12 16 0.5 0.5 0.06
4 > 128 32 2 0.12
0.25 22.63 1.45 0.47 0.08
Acinetobacter spp.
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
(10)
Antibiotic
0.03->32 0.25->32 0.03->32 0.03->32 0.015->32
90%
32 32 4 8 2
32 >32 >32 >32 32
6.00 27.90 2.60 5.60 3.50
P. aeruginosa (10)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
>32 >32 >32 >32 >32
>32 >32 >32 >32 >32
>32 >32 >32 >32 >32
>32 >32 >32 >32 >32
X. maltophilia (10)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.5->32 8->32 2->32 4->32 1->32
32 >32 >32 >32 32
>32 >32 >32 >32 >32
14.90 >32 26.00 >32.00 19.70
Pseudomonas spp.
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
2->32 >32 8->32 16->32 1->32
>32 >32 >32 >32 >32
>32 >32 >32 >32 >32
>32 >32 >32 >32 27.90
H. influenzae (35)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.015-0.03 1-4 0.06-0.25 0.015 0.015-0.25
0.03 1 0.25 0.015 0.06
0.03 2 0.25 0.015 0.12
0.03 1.43 0.21 0.02 0.08
N. gonorrhoeae (29)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.015-0.12 0.12-2 0.015-0.5 0.015-0.12 0.015-0.12
0.015 0.12 0.015 0.015 0.015
0.015 1 0.03 0.015 0.03
0.02 0.16 0.02 0.02 0.02
Staphylococcus aureus
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
32->32 0.6->32 16->32 2->32 16->32
>32 8 >32 8 32
>32 32 >32 >32 32
>32 6.70 >32 10.70 30.20
8->32 0.25-32 8->32 1->32
32 4 32 4
>32 16 >32 >32
30.20 2.30 28.80 6.50
(10)
(12)
S. epidermidis (13)
Ceftibuten Cefaclor Cefetamet Cefteram
L. Verbist et al.
58
TABLE 2.
Continued MIC (~g/ml)
Microorganism (no. of isolates)
Streptococcus agalactiae (11)
Antibiotic
Range
50%
90%
Geometric Mean
Tigemonam
4-32
32
32
24.50
16
32
19.30
1
4
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
16-32 1-4 4-16 0.03-1 32->32
S. pneumoniae (12)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
1-2 0.12-0.25 0.25-0.5 0.015 2-8
2 0.25 0.25 0.015 4
2 0.25 0.6 0.015 8
1.78 0.22 0.35 0.02 4.76
S. pyogenes (10)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
0.5 0.12-0.25 0.06 0.015-0.06 1
0.5 0.25 0.06 0.015 1
0.5 0.25 0.06 0.015 1
0.50 0.19 0.06 0.02 1.00
Enterococcus (10)
Ceftibuten Cefaclor Cefetamet Cefteram Tigemonam
>32 32->32 >32 >32 32->32
active than cefteram against Klebsiella spp. and Providencia spp. Cefteram, in turn, demonstrated greater activity than cefetamet against E. coli, M. morganii, P. mirabilis, and Y. enterocolitica. To assess the overall antimicrobial activity of these agents, we calculated geometric mean MICs of each antibiotic for the Enterobacteriaceae. Overall activity was comparable for ceftibuten and tigemonam (geometric mean MIC = 0.30 g,g/ml and 0.20 p~g/ml, respectively), but was about 4-9 times greater than that of cefetamet and cefteram (geometric mean MIC = 1.72 ~,g/ml and 1.24 ~g/ml, respectively). Cefetamet and cefteram demonstrated similar overall activity. The activity of cefador was comparatively poor (geometric mean MIC = 30.19 ~g/ml). Ceftibuten at a concentration of 48 ~g/ml inhibited 85% of multiply-resistant enterobacteria. For the most part, this level of antimicrobial activity was superior to that observed with the comparative compounds. Only 37% of these enteric bacilli were susceptible to cefaclor (48 ~g/ml), 69% to cefetamet (44 ~g/ml), 59% to cefteram (41 ~g/ml), and 95% to tigemonam (48 ~g/ml). Susceptible breakpoints used were those defined by the NCCLS for compounds closely related to ceftibuten, cefetamet, cefteram, and tigemonam, that is, cefaclor, cefuroxime axetil, ce-
8 0.06 32
>32 >32 >32 >32 >32
16 0.5 32
>32 >32 >32 >32 >32
1.46
7.51 0.09 >32
>32 >32 >32 >32 >32
fixime, and aztreonam. The percentages of enterobacteria that were susceptible to other alternative breakpoint concentrations of 42, 4, and 8 ~g/ml are compared in Table 3. The susceptibility of cefuroxime- and cefotaximeresistant strains of Enterobacteriaceae to ceftibuten, cefetamet, cefteram, and tigemonam was determined. The findings are presented in Table 4. Cefuroxime-susceptible strains were most susceptible to the new oral [3-1actam compounds, as compared to cefuroxime- and cefotaxime-resistant strains. Susceptibility to ceftibuten, cefetamet, cefteram, and tigemonam decreased slightly among those strains that were resistant to cefuroxime, but susceptible to cefotaxime. Susceptibility decreased fiLrther among the cefotaxime-resistant bacteria. This decrease in activity occurred with all four antibiotics, but not to the same extent. Based on the ratio of the geometric mean MIC for cefotaxime-resistant strains to the geometric mean MIC for cefuroxime-susceptible strains, activity decreased -60-100 times with ceftibuten, cefetamet, and cefteram; a 20-fold decrease was observed with tigemonam. These results may suggest that tigemonam is less affected by some resistance mechanisms (f~-lactamases or permeability mutations) than ceftibuten, cefetamet, or cefteram.
59
Ceftibuten Activity in Belgium
TABLE 3.
Susceptibility of 813 Clinical Isolates to Ceftibuten, Cefaclor, Cefetamet, Cefteram, a n d T i g e m o n a m at Concentrations of 4 2 , 4 4 , a n d 4 8 ~g/ml % Susceptible to Concentration of Antibiotic in ~g/ml Ceftibuten
Cefaclor
Cefetamet
Cefteram
Tigemonam
Microorganism (no. of isolates)
42
44
48
42
~4
48
42
44
48
~2
~4
~8
42
44
48
Enterobacteriaceae
77
80
85
19
28
37
64
69
75
68
74
79
90
93
95
40
40
40
20
20
20
0
50
70
30
40
40
50
50
50
13
13
13
0
0
0
7
7
13
0
3
7
13
13
17
100 100 0
100 100 0
100 100 8
97 100 36
100 100 52
100 100 76
100 100 0
100 100 0
100 100 12
100 100 24
100 100 44
100 100 68
100 100 0
100 100 0
100 100 8
51
51
51
72
77
77
51
58
72
77
77
77
30
37
51
(641)
Acinetobacter spp. (lO)
Pseudomonas spp. ~ (30)
H. influenzae (35) N. gonorrhoeae (29) Staphylococcus spp. (25)
Streptococcus spp. (43)
qncludes X. maltophilia;
Activity Against H. influenzae and N.
lower than those specified by the N C C L S breakpoints for similar c o m p o u n d s (NCCLS, 1990).
gonorrhoeae Ceftibuten, cefetamet, cefteram, and tigemonam were very active against strains of H. influenzae a n d N. gonorrhoeae. To exemplify, the MIC9o of ceftibuten was 4 0 . 0 3 ~g/ml for b o t h of these species. Cefaclor w a s less active t h a n the comparative c o m p o u n d s against these species. As is evident in Tables 2 a n d 3, 100% of strains of b o t h species were susceptible to each of the c o m p o u n d s at concentrations that were TABLE 4.
Activity Against Staphylococcus and
Streptococcus s p p .
Staphylococci were almost completely resistant to the n e w beta-lactam c o m p o u n d s . The MICs0s for strains of Staphylococcus aureus a n d Staphylococcus epidermidis were in the resistant range for ceftibuten, cefetamet, cefteram, a n d t i g e m o n a m . Cefaclor was
Susceptibility of Enterobacteriaceae to Ceftibuten, Cefetamet, Cefteram, a n d T i g e m o n a m Categorized b y their Susceptibility/Resistance to Cefuroxime a n d Cefotaxime Cumulative Percentage of Strains Inhibited by Concentration of Antibiotic in ~g/ml
Strain (no. of isolates)
Antibiotic
0.015 0.03 0.06 0.12 0.25 0.5
1
2
4
8
96 92 97 98
98 94 98 99
99.1 97 99 99.1
Cefuroxime-susceptible a Ceftibuten (334) Cefetamet Cefteram Tigemonam
28 -2 26
42 3 5 32
53 11 17 44
74 29 32 57
86 44 55 87
90 94 68 84 76 89 95 97
Cefuroxime-resistantb (198)
Ceftibuten Cefetamet Cefteram Tigemonam
17 --18
31 --30
37 -3 38
44 6 15 43
53 19 22 58
Cefotaxime-resistant~ (109)
Ceftibuten Cefetamet Cefteram Tigemonam
-. . --
-. . --
3
15
. . 1
17
-. .
. . --
~Strains susceptible to cefuroxime 48 ~g/ml. bStrains resistant to cefuroxime, but susceptible to cefotaxime ~8 ~g/rnl. cStrains resistant to cefotaxime.
16
32
Geometric Mean MIC
9 9 . 1 99.1 99 100 99 99.7 99.1 99.7
0.08 0.43 0.31 0.10
60 64 69 71 78 27 38 50 57 63 29 40 56 67 75 74 85 90 94 97
90 70 83 98
91 76 94 99
0.48 3.86 2.24 0.21
25 30 37 1 2 6 1 1 4 31 51 64
56 33 27 93
65 43 38 98
6.74 25.13 30.80 1.88
42 19 12 74
52 30 24 79
60
the most active of the agents evaluated against staphylococci and inhibited 58% and 92% of strains of S. aureus and S. epidermidis, respectively. Table 3 shows the low percentage of staphylococci, in general, inhibited by concentrations of ~2, 4, and 8 p~g/ml. Against streptococci, cefteram was the most active and tigemonam the least active of the antimicrobial agents tested (Table 2). Ceftibuten was highly active against strains of Streptococcus pyogenes; the MIC9o was 0.5 p,g/ml. Against Streptococcus pneumoniae, the MIC90 of ceftibuten was 2 p~g/ml. Strains of Streptococcus agalactiae (serogroup B) were uniformly resistant to inhibition by ceftibuten and tigemonam, and most strains of this species were resistant to cefetamet, as well. Cefteram exhibited the greatest inhibitory activity against this species (MIC90 = 0.5 ~g/ml), as compared to cefaclor (MIC90 = 4 p~g/ml). Strains of E. faecalis were consistently resistant to all of the antibiotics tested. The percentages of streptococci that were susceptible to each of the compounds at various breakpoints are shown in Table 3.
Activity Against Other Microorganisms Isolates of Pseudomonas aeruginosa were uniformly resistant to all of the compounds evaluated. Against strains of Pseudomonas maltophilia, other Pseudomonas spp. and Acinetobacter spp., the activity of all agents was minimal and limited to inhibition of a few unusually susceptible isolates, particularly among the Acinetobacter spp. DISCUSSION It has long been recognized that bacteria are especially adept at developing resistance to antibiotics (Neu, 1984). In fact, resistant microorganisms appear to arise as quickly as new antimicrobial agents are introduced (Lafong and Murphy, 1986). Thus, intensive research continues in an effort to develop antibiotics that will inhibit multiply-drug-resistant pathogens. Ceftibuten is a new, nonesterified, orally active cephem antibiotic with excellent pharmacokinetic properties (Nakashima et al., 1988) and potent activity against a wide range of Gram-negative and
L. Verbist et al.
selected Gram-positive bacteria (Hamashima et al., 1987; Jones and Barry, 1988a). In this present study, we compared the in vitro activity of ceftibuten with that of other orally active ~-lactam compounds: cefaclor, a first-generation cephalosporin; cefetamet and cefteram, two esterified cephems currently under evaluation; and tigemonam, a recently investigated monobactam. Ceftibuten, cefetamet, cefteram, and tigemonam were much more active than cefaclor against multiply-resistant Enterobacteriaceae, and ceftibuten and tigemonam were the most active of the agents tested. Also, all of the new agents exhibited excellent activity against multiply-resistant strains of H. influenzae and N. gonorrhoeae and were somewhat more active than cefaclor against these species. Against staphylococcal isolates, cefaclor was far more active than any of the comparative compounds. Moreover, the new [3-1actam agents generally exhibited no better activity than cefaclor against streptococcal strains, except for cefteram. Strains of E. faecalis and P. aeruginosa were consistently resistant to inhibition by all of the agents evaluated, and none of the compounds had any useful activity against isolates of other Pseudomonas spp. or Acinetobacter spp. Our study of the comparative in vitro activity of ceftibuten confirms the findings of other researchers (Jones and Barry, 1988a-d; Shawar et al., 1989). Ceftibuten has potent activity against many members of the Enterobacteriaceae, H. influenzae, N. gonorrhoeae, and S. pyogenes, and many of these microorganisms demonstrate resistance to multiple antibiotics (Jones and Barry, 1988a--d; Shawar et al., 1989). Ceftibuten also has proven to be highly active against strains of Moraxella (Branhamella) catarrhalis, and Neisseria meningitidis in other studies (jones and Barry, 1988a-c). Based on these data, ceftibuten may be indicated in the treatment of patients with urinary tract infections caused by most Enterobacteriaceae, genital infections caused by pathogenic Neisseria spp. and lower and upper respiratory tract infections caused by such organisms as H. influenzae, M. catarrhalis, most pneumococci, and B-hemolytic streptococci.
This study was supported by a grant from Schering Corporation and a grant from E.R. Squibb and Sons.
Ceftibuten Activity in Belgium
61
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